Affluent people of modern time have greater awareness on life quality enhancing activities such as leisure activities and exercises. Many people these days lack enough exercises and exercise space. To overcome these constraints many exercise equipments and fitness facilities have been developed that take smaller space and are simple in use.
For instance U.S. Pat. No. 7,766,795 discloses a trampoline system which includes a circular frame supported by a plurality of legs. The circular frame is coupled with a rebounding mat through a plurality of spring members and a cylindrical wall made of a resilient net to prevent users from being thrown outside the trampoline when in use. When a user jumps and rebounds from the mat the spring members are stretched by the weight of the user and mat. The spring members have other ends connected to the circular frame which receives the forces transferred from the spring members. When in use the support structure, including the circular frame and legs, have to bear significant pressure.
U.S. publication 2010/0273611 discloses another type of trampoline. The pressure of springs levied on the circular frame is discussed as follow. Its FIG. 3 shows the connection relationship between the spring and frame. The spring has one end latched on the frame at an upper side close to the inner side. When a user jumps on the trampoline the spring stretches the frame. Based on mechanics the stretching force of the spring is divided into a horizontal component and a vertical component. The mat of the trampoline sinks under user's weight, and the force of the vertical component levied on the frame is much greater than that of the horizontal component. I.e., the frame, aside from receiving the inward stretching force, also receives a great vertical pressure.
In theory, multi-directional stresses exerted onto a frame made of circular tubes can offset each other. The frame made of circular tubes has many advantages, such as lower cost and easy assembly. But research and use experiences show that the spring exerts unidirectional force on the frame. The stretching force of the spring exerted onto the tubular frame is fixed in location and direction. The tubular frame cannot effectively offset or distribute the received stress. After used for a period of time junctions of the frame tend to deform due to the pressure caused by user's jumping. The upper side and lower side of the circular tube receive more stress under the stretching of the spring onto the frame. Moreover, the circular frame usually is made by coupling a plurality of tubes, and the junctions of the tubes are the most fragile spots while the received stress is greatest. Thus deformation easily takes place after used for a prolonged period of time and the concern of safety deficiency arises.
Most known conventional trampolines adopt the frame of circular tubes. Besides the aforesaid U.S. Pat. No. 7,766,795 and U.S. publication 2010/0273611, U.S. Pat. No. 7,854,687 and U.S. publication Nos. 2010/0311545 and 2010/0190608 and China Patent CN2571421 also disclose trampolines using the frame of circular tubes.
In order to improve physical strength, aside from the frame of circular tubes, other frame alterations have been made, such as U.S. publication 2010/0240496. Its FIG. 3 shows that the tubular junctions of the frame are formed with flat surfaces on the upper and lower surfaces and arched coupling surfaces between the upper and lower flat surfaces in a deformed quadrilateral like a race track to provide support and enhance physical strength.
However, in order to increase the lifespan of trampoline and enhance user's safety during use, there is still room for improvement in terms of the structural design of the circular frame, especially on the tubular junctions, to make sure that sufficient stress-withstanding strength is provided, and tight coupling of tubes is formed to improve durability of trampoline.